X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.122] verified) by logan.com (CommuniGate Pro SMTP 5.3.9) with ESMTP id 4489098 for flyrotary@lancaironline.net; Fri, 01 Oct 2010 10:41:10 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.122; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=lu/RhtYP0ChAeUxMEPBris12a71TWT5f9yvo3GNwP9w= c=1 sm=0 a=aEyEvGi4rrIA:10 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=pedpZTtsAAAA:8 a=Ia-xEzejAAAA:8 a=7g1VtSJxAAAA:8 a=3xaNd7muDMnC6mx0BZ8A:9 a=4kUd1HnIvo4_EPR-xuMA:7 a=8pz9rKcUs-hqGh80Rzarlfyg3uMA:4 a=wPNLvfGTeEIA:10 a=Qa1je4BO31QA:10 a=eJojReuL3h0A:10 a=EzXvWhQp4_cA:10 a=giCQLef0PnXPyTZ1Y1gA:9 a=NZIQnfhw19L0cDZOJDoA:7 a=Ros3UzSN2lNmdiVxS_3KcvUgNh4A:4 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:50128] helo=EdPC) by cdptpa-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id F6/A2-14228-4E2F5AC4; Fri, 01 Oct 2010 14:40:36 +0000 Message-ID: From: "Ed Anderson" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: SAG from Paducah Date: Fri, 1 Oct 2010 10:40:23 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0029_01CB6155.0D4F0CF0" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_0029_01CB6155.0D4F0CF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Charlie, I agree with your assessment. Certainly is possible to have pre-ignition without detonation. = Pre-ignition simply means something is firing the combustible mixture = before its intended ignition point - most of the time this is caused by = some element (carbon, metal) retaining sufficient heat and temperature = from the last combustion event to prematurely fire the next combustion = event. Pre-ignition generally results in higher combustion chamber pressure and = heat as frequently the combustion event is started long before its = intended and may occur as the piston/rotor is coming up on its = compression stroke. The piston trying to compress this burning mixture = adds to the pressure and heat load. Continued pre-ignition continues = to build up the heat load until seals, sparkplugs, etc start to = deteriorate - if continued it frequently leads to detonation which can = quickly lead to destruction of the engine (at least in piston engines). = So pre-ignition can raise indeed raise coolant temps due to this = increased heat load. When the combination of heat load and pressure = reaches a certain point the combustible mixture can explode rather than = burn - detonation has begun. Detonation does not necessarily add greatly to the heat load above that = already caused by pre-ignition - but since detonation is essentially a = situation where the combustible mixture is no longer burning but = actually exploding. The combination of elevated heat/temperature and = shock of this exploding (rather than burning) mixture can in short order = destroy an engine. Now our rotary engines appear to be less prone to detonation and the = quenching effect of its less efficient combustion chamber shape may be = to our advantage in this case. I have experience SAG a number of times = and I never got the impression the engine was under stress (same can not = be said for me), in fact if anything the lesser rpm and EGT always let = me to believe it was producing less power and therefore under less = stress. In otherwords, my impression was the problem was the engine was = failing to light off the combustible mixture and therefore was producing = less power (and thereby less stress on the engine). So while something = to be concerned about, I had not felt SAG was dangerous (other than to = seat cushions). I have had detonation completely destroy my spark plugs in very short = order - but, it took extreme missetting of my static ignition point to = do this. I have never detected any damage (even to the plugs) through = the normal SAG event. So in our case, I guess its possible that = pre-ignition in the rotary is not as conducive to detonation - or = perhaps we are not getting pre-ignition? It's always great to understand what is happening to our engines - but, = regardless of the ultimate cause of SAG, we do know that replacing the = plugs does provide a fix (if only temporarily {:>)) and a fairly = inexpensive one. I am awaiting Steve's experiment with colder plugs - = even extending the my current SAG interval from 25- 50 hours would be = worthwhile That's my take on it. Ed -------------------------------------------------- From: "Charlie England" Sent: Friday, October 01, 2010 9:59 AM To: "Rotary motors in aircraft" Subject: [FlyRotary] Re: SAG from Paducah >=20 > I've only been scanning this series of emails, but it looks like both=20 > terms pre-ignition & detonation have been applied to the SAG symptom.=20 > Isn't it possible to have pre-ignition (causing elevated water temps,=20 > etc and declining EGT) without detonation, and the resulting = destruction=20 > of plugs, seals, etc? >=20 > Charlie >=20 > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html > ------=_NextPart_000_0029_01CB6155.0D4F0CF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Charlie, I agree with your=20 assessment.

Certainly is possible to have pre-ignition without=20 detonation.  Pre-ignition simply means something is firing the = combustible=20 mixture before its intended ignition point - most of the time this is = caused by=20 some element (carbon, metal) retaining sufficient heat and temperature = from the=20 last combustion event to prematurely fire the next combustion=20 event.

Pre-ignition generally results in higher combustion = chamber=20 pressure and heat as frequently the combustion event is started long = before its=20 intended and may occur as the piston/rotor is coming up on its = compression=20 stroke.  The piston trying to compress this burning mixture adds to = the=20 pressure and heat load.   Continued = pre-ignition=20 continues to build up the heat load until seals, sparkplugs, etc start = to=20 deteriorate - if continued it  frequently leads to detonation = which=20 can quickly lead to destruction of the engine (at least in piston=20 engines).   So pre-ignition can raise indeed raise coolant = temps due=20 to this increased heat load.  When the combination of heat load and = pressure reaches a certain point the combustible mixture can explode = rather than=20 burn - detonation has begun.

Detonation does not necessarily add = greatly=20 to the heat load above that already caused by pre-ignition - but since=20 detonation is essentially a situation where the combustible mixture is = no longer=20 burning but actually exploding.  The combination of elevated=20 heat/temperature  and shock of this exploding = (rather than=20 burning) mixture can in short order destroy an engine.

 Now = our=20 rotary engines appear to be less prone to detonation and the quenching = effect of=20 its less efficient combustion chamber shape may be to our advantage in = this=20 case.   I have experience SAG a number of times and I never = got the=20 impression the engine was under stress (same can not be said for me), in = fact if=20 anything the lesser rpm and EGT always let me to believe it was = producing less=20 power and therefore under less stress.  In otherwords, my = impression was=20 the problem was the engine was failing to light off the combustible = mixture and=20 therefore was producing less power (and thereby less stress on the=20 engine).  So while something to be concerned about, I had not felt = SAG was=20 dangerous (other than to seat cushions).

I have had detonation = completely=20 destroy my spark plugs in very short order - but, it took extreme = missetting of=20 my static  ignition point to do this.  I have never detected = any=20 damage (even to the plugs) through the normal SAG event.  So in our = case, I=20 guess its possible that pre-ignition in the rotary is not as conducive = to=20 detonation - or perhaps we are not getting pre-ignition?

It's = always=20 great to understand what is happening to our engines - but, regardless = of the=20 ultimate cause of SAG, we do know that replacing the plugs does provide = a fix=20 (if only temporarily {:>)) and a fairly inexpensive one.  I am = awaiting=20 Steve's experiment with colder plugs - even extending the my current SAG = interval from 25- 50 hours would be worthwhile

That's my take on=20 it.

Ed

--------------------------------------------------From:=20 "Charlie England" <ceengland@bellsouth.net>
Sent: Friday, = October 01,=20 2010 9:59 AM
To: "Rotary motors in aircraft"=20 <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: SAG from = Paducah

>
> I've only been scanning this series of = emails, but=20 it looks like both
> terms pre-ignition & detonation have = been=20 applied to the SAG symptom.
> Isn't it possible to have = pre-ignition=20 (causing elevated water temps,
> etc and declining EGT) without=20 detonation, and the resulting destruction
> of plugs, seals, = etc?
>=20
> Charlie
>
> --
> Homepage: =20 http://www.flyrotary.com/
> Archive and UnSub:  =20 http://mail.lancaironline.net:81/lists/flyrotary/List.html
>= ------=_NextPart_000_0029_01CB6155.0D4F0CF0--